After weeks of devastating losses, the stock market posted its second-biggest one-day point gain yesterday, cheering the hearts and wallets of investors.

The value of portfolios was boosted by $500 billion in just seven hours.

The Dow Jones industrial average rocketed 488.95 points, or 6.35 percent, to 8,191.29. That jump erased the losses of the past three trading sessions.

But Wall Street pros and individual investors remained confused about whether the big rally – which took place before news came out that AOL Time Warner is the latest target of investigators – meant the market had already bottomed.

“I’m actually planning to sell my car and put some money in the market,” said Mike Martone, a 22-year-old customer-service rep who lives in Rockland County. “This makes me much more confident now.”

But Gloria Collado, a 36-year-old concierge, disagreed.

“You should still take your money and put it under the mattress,” the Queens woman said. “This isn’t a sign of good things to come.”

Wall Street experts were similarly confused.

“My sense of history is that even if the overall market has not yet hit bottom, it is close, and maybe 15 to 20 percent of all stocks already have made their lows,” said Donald Straszheim, president of Straszheim Global Advisors.

“It’s a good bounce and investors should be happy,” said Daniel Strachman, author of “Essential Stock Picking Strategies.”

“But a one-day move does not a trend make,” he added. “The market is continuing to search for a bottom, and investors need to be aware of that.”

Buyers ignored the potential for further downturns, focusing instead on the bargain prices on many stocks.

“Some of the best companies in the world are available at prices we haven’t seen in 15 years,” said Mark Petrie, a portfolio manager at Hokanson Capital Management.

All the buying boosted the broad market averages in the United States.

The technology-packed Nasdaq composite, which had its worst percentage loss ever just one day earlier, added 61.18, or 4.98 percent, to 1,290.23 yesterday.

The S&P 500 index rose 45.73, or 5.73 percent, to 843.43.

“I’m very optimistic about this,” said Kim Mancuso, 30, a Brooklyn resident who works as a technical engineer at NBC. “In this case, what goes down must come up. So this is a beginning sign of some positive potential.”

But older investors, who do not have time to ride out market turmoil, remained bearish.

“I don’t think today signifies an upward trend,” said Sean Durkin, 55, an alternative healing specialist who was visiting New York from Portland, Oregon.

“I’ll feel much better about things when these guys are all in prison,” he said, referring to the white-collar fraud suspects at Enron and other scandal-plagued companies. It all added up to the busiest day ever at the New York Stock Exchange, where 2.7 billion shares changed hands.